Culver horse tests positive for West Nile virus

A Bend equine veterinary clinic says it has diagnosed a case of equine West Nile virus in a horse from the Jefferson County town of Culver, the third so far in Oregon this year.

In a posting to its Facebook page, Bend Equine Medical Center said the owners of the horse had not yet been reached, but “we feel it is important to let our clients know.”

So far, there have been two other cases of WNV found in Oregon horses so far this year, both in northeast Oregon (Baker and Union counties).

Clinic veterinarian Dr. Wendy Krebs said this was apparently the first equine West Nile case in Central Oregon in recent years. The horse from Culver had not traveled anywhere else, she said, and was not vaccinated for the virus.

“It was hospitalized over the weekend and went home doing fairly well early this week,” she said by e-mail.

West Nile virus is the leading cause of arbovirus encephalitis in horses and humans in the country, the clinic noted in its Facebook posting.

Since 1999, over 25,000 cases of West Nile virus encephalitis have been reported in U.S. horses. Horses represent nearly 97 percent of all reported non-human mammalian cases of WNV disease.

The virus is transmitted from avian reservoir hosts by mosquitoes (and infrequently by other bloodsucking insects) to horses, humans and a number of other mammals.

Horses and humans are considered to be dead-end hosts for WNV; the virus is not directly contagious from horse to horse or horse to human, they noted.

Indirect transmission via mosquitoes from infected horses is highly unlikely, said Krebs, as these horses do not circulate a significant amount of virus in their blood.

The case fatality rate for horses exhibiting clinical signs of WNV infection is approximately one-third, she added. However, data has shown that 40 percent of horses that survive the acute illness caused by WNV still exhibit residual effects, such as gait and behavioral abnormalities.

Annual vaccination for West Nile virus is recommended as a core vaccine and is an essential standard of care for all horses in North America, Krebs said.

The facility also posted more vaccination guidelines Saturday from the American Association of Equine Practitioners on its .

You can learn more about West Nile virus and the latest tracking reports at this Oregon Health Authority Website.

There have been four presumptive cases of West Nile in humans this year, the agency reports, and 31 confirmed in mosquitoes